1. Field of the Invention
The present invention relates generally to electrolytic pool chlorinators for chlorinating a pool of water, and more particularly, to an electrolytic pool chlorinator having a baffled cathode chamber into which chlorinated pool water is delivered for preventing caustic concentrations within the catholyte from becoming excessively high while maintaining good current efficiency and rapid start-up.
2. Description of the Prior Art
Electrolytic pool chlorinators are well known in the art and are exemplified by the apparatus described in U.S. Pat. Nos. 914,856, issued to Meyer; 3,223,242, issued to Murray; 4,229,272, issued to Yates; 4,129,493, issued to Tighe, et al.; 4,136,005, issued to Persson, et al.; 4,290,873, issued to Weaver; 4,500,404, issued to Tucker; 3,563,879, issued to Richards, et al.; as well as U.S. Pat Nos. 4,472,256 and 4,599,159 issued to the present applicant. Such electrolytic pool chlorinators generally operate by electrolyzing a sodium chloride brine solution contained within an anode chamber, attracting positively-charged sodium ions to a negatively-charged cathode, and attracting negatively-charged chloride ions to the positively-charged anode, thereby liberating chlorine gas at the anode. The chlorine gas released thereby may then be used to chlorinate the water within a swimming pool, spa or the like.
The anode and cathode chambers of such an electrolytic pool chlorinator are typically separated from one another by an ion-permeable barrier to prevent the chlorine gas liberated within the anode chamber from mixing with the hydrogen gas liberated in the cathode chamber and to physically separate the sodium chloride (or brine) anolyte solution within the anode chamber from the sodium hydroxide (caustic soda) catholyte solution within the cathode chamber. The ion-permeable membrane is permeable to positive ions, such as sodium ions formed within the anode chamber, but presents a barrier to the passage of negative ions, such as hydroxyl ions, present within the cathode chamber, at least at relatively low concentrations of such hydroxyl ions.
Ion selective membranes used to separate the anode and cathode cells, such as "NAFION" brand perfluorosulfonic acid membrane commercially available from E. I. DuPont de Nemours and Company of Wilmington, Del., form imperfect ion barriers. Hydroxyl ions within the catholyte can migrate through such ion selective membranes into the anolyte both during periods when the chlorinator is operating, as well as during periods when the chlorinator is shut off. As the concentration of hydroxyl ions within the catholyte becomes greater, back-migration of hydroxyl ions through the ion permeable selective membrane increases. If the sodium hydroxide concentration with the catholyte accumulates to within the range of 15% to 20%, the back-migration of hydroxyl ions into the anolyte is approximately 10% of the total number of hydroxyl ions within the catholyte during chlorinator operation. By comparison, dropping the sodium hydroxide concentration of the catholyte to the range of 1%-3% decreases the rate of back-migration of hydroxyl ions to approximately 2%. While the rate of back-migration of hydroxyl ions is lessened when the chlorinator is shut off, migration of hydroxyl ions into the anolyte during shut off is still significant, particularly since an electrolytic pool chlorinator used with a typical backyard swimming pool is shut off for greater periods of time each day then it is turned on.
Back-migration of hydroxyl ions into the anolyte is undesirable for several reasons. Hydroxyl ions passing into the anolyte initially form hypochlorites and, in a subsequent step, form chlorates, such as sodium chlorate (NaClO.sub.3) in the anolyte. Such chlorates accumulate over time within the brine solution, and, at very high concentrations, form a chlorate-saturated brine solution which reduces the amount of sodium chloride that can be dissolved within the anolyte, thereby minimizing further chlorine production. Furthermore, passage of hydroxyl ions into the anolyte reduces chlorine gas production because chlorine which combines with hydroxyl ions to form hypochlorites is prevented from being liberated as chlorine gas. In addition, the presence of hydroxyl ions within the anolyte can lead to passivation of the dimensionally stable anode material resulting from increased oxidation which occurs at high pH within the anolyte. Hydroxyl ions within the anolyte also contribute to the formation of calcium deposits upon the anode side of the ion-permeable membrane, which deposits lead to the plugging of the membrane and a corresponding reduction in the efficiency of the chlorinator.
In U.S. Pat. No. 4,040,919 issued to Eng, it is proposed that hydrochloric acid be periodically added to the anolyte for eliminating chlorates and dissolving calcium deposits upon the ion permeable membrane. However, the addition of hydrochloric acid to the chlorates within the anolyte instantly produces large quantities of poisonous chlorine gas, and is therefore a dangerous procedure to perform. The typical owner of a backyard swimming pool could not be expected to add acid to the anolyte in the manner taught by Eng without posing a substantial safety risk.
Within applicant's U.S. Pat. No. 4,599,159, an electrolytic pool chlorinator is disclosed wherein pool water is continuously delivered to the cathode chamber at a point relatively remote from the cathode to continuously dilute the catholyte. An overflow conduit communicating with the cathode chamber continuously drains catholyte from the cathode chamber to prevent excess concentrations of sodium hydroxide from accumulating therein. While maintaining a relatively low sodium hydroxide concentration within the cathode chamber minimizes undesired back-migration of hydroxyl ions into the anolyte, the reduced hydroxyl ion concentration in the catholyte causes the chlorinator to take longer to start up after it has been shut off for a period of time, since there are relatively few ions in the vicinity of the cathode upon initial start-up which can conduct an electrical current. In contrast, a higher concentration of hydroxyl ions in the catholyte increases the electrical conductivity thereof and results in more efficient short term chlorine production. Moreover, if the concentration of sodium hydroxide within the catholyte is very low, then any metal hardness ions (such as calcium or magnesium) introduced into the cathode chamber (as by the addition of pool water thereto) are more likely to reach the cathode and/or ion permeable membrane before such metal hardness ions precipitate out as a deposit. Such precipitates include calcium carbonate (CaCO.sub.3), calcium hydroxide (Ca(OH).sub.2), and magnesium hydroxide (Mg(OH).sub.2), and are more likely to form deposits at the higher pH conditions proximate the cathode. Such deposits upon the cathode and/or membrane reduce the efficiency of the chlorinator and require more frequent maintenance.
Accordingly, it is an object of the present invention to provide an electrolytic pool chlorinator which minimizes back-migration of hydroxyl ions from the catholyte into the anolyte, while at the same time, maintaining a sufficiently high concentration of hydroxyl ions in the vicinity of the cathode to permit quick start-up following periods when the chlorinator is shut off and permitting good electrical conductivity for efficient chlorine production.
It is another object of the present invention to provide such a chlorinator which prevents excessive concentrations of hydroxyl ions from accumulating within the catholyte while simultaneously minimizing the possibility of metal hardness ions within the catholyte from precipitating out and depositing upon the cathode and/or ion permeable membrane.
It is a further object of the present invention to permit the use of relatively hard pool water to dilute the catholyte while avoiding deposits of metal hardness ion compounds upon the cathode and/or ion permeable membrane, despite the relatively high concentrations of metal hardness ions typically present within such pool water.
It is a still further object of the present invention to provide an electrolytic chlorinator that is relatively free of routine maintenance at frequent intervals.
As mentioned above, the formation of metal hardness deposits upon the cathode are to be avoided in order to maintain good electrical conductivity for the chlorinator. Nonetheless, some metal hardness ions added to the catholyte tend to diffuse toward the vicinity of the cathode. Metal hardness ion deposits, such as calcium hydroxide (Ca(OH).sub.2) and magnesium hydroxide (Mg(OH).sub.2), are particularly a problem when pool water is used to dilute the catholyte, since pool water typically contains from 300 to 2000 parts per million of calcium and magnesium.
It is therefore another object of the present invention to reduce the likelihood that any metal hardness ions reaching the vicinity of the cathode will precipitate out and deposit upon the cathode.
As explained above, were chlorates to form and accumulate within the anode chamber, the efficiency of the chlorinator would be reduced. In addition, metal hardness ions within the anolyte can be precipitated as deposits upon the ion permeable membrane, plugging the membrane and further reducing the efficiency of the chlorinator. While such accumulations of chlorates and metal hardness ions can be eliminated by periodic draining of the brine tank, this would require the operator to perform additional maintenance steps.
It is therefore a further object of the present invention to provide an electrolytic chlorinator which serves to prevent accumulations of chlorates and metal hardness ions within the anolyte without requiring the operator to perform additional maintenance steps beyond merely refilling the brine tank with salt.
When chlorine gas is reacted with pool water to chlorinate the same, both hypochlorous acid and hydrochloric acid are produced. Hypochlorous acid is a desired sanitizing agent which kills bacteria and algae in the pool water. On the other hand, hydrochloric acid merely tends to lower the pH of the pool water. While it may be advantageous to briefly maintain chlorinated pool water at a lowered pH to superchlorinate the water, pool water maintained at a pH below 7.0 can cause swimmer discomfort and can cause corrosion of metal fixtures.
Accordingly, it is another object of the present invention to provide such an electrolytic pool chlorinator wherein hydrochloric acid produced upon reaction of chlorine gas with pool water is at least partially neutralized before being returned to the pool.
While some electrolytic pool chlorinators are installed at the time that the swimming pool is constructed, it is more often the case that such electrolytic pool chlorinators are installed with existing swimming pool equipment. For new swimming pool installations, a gravity feed line can be installed from the outlet of the chlorinator to the skimmer of the pool in order to permit chlorinated water to drain back to the pool under the force of gravity. However, when an electrolytic pool chlorinator is added to existing swimming pool equipment, gravity feed of the chlorinated water output from the chlorinator back to the pool is often not possible without breaking the concrete pool decking surrounding the pool in order to lay such a gravity feed line back to the pool. In such cases, it is possible to return the chlorinated water to the swimming pool by coupling the outlet of the chlorinator to the suction side of the pool pump. However, one disadvantage of this technique is that the pool pump can lose its prime if, for some reason, the flow of chlorinated water produced by the electrolytic pool chlorinator is either interrupted while the pool pump is operating or is of a lesser flow rate than the rate at which such chlorinated water is being suctioned back to the pump. If air permitted to enter the pool pump instead of chlorinated water, the pump may lose its prime.
Accordingly, it is an object of the present invention to provide an electrolytic pool chlorinator having a chlorinated water outlet that can be coupled to the suction inlet of the pool pump for returning chlorinated water to the pool without permitting the pool pump to lose its prime.
In designing an electrolytic pool chlorinator, it is desirable to locate the cathode chamber at a lowermost point within the chlorinator housing so that the upper portion of the chlorinator can be utilized to store salt and water to form the brine solution supplied to the anode chamber. The larger the space available to fill the brine tank of the chlorinator with water and salt, the less often that the user needs to add salt or water thereto. On the other hand, after long periods of operation, the cathode chamber may need to be rejuvenated, as by addition acid to remove any deposits which may have formed over extended periods within the cathode chamber. In known electrolytic pool chlorinators, such servicing of the cathode chamber is difficult and typically requires that the chlorinator be disassembled in order to gain access to the cathode chamber. Such disassembly typically requires that the brine tank first be drained, thereby wasting the contents thereof. In addition, during colder winter month, it is desirable to fill the cathode chamber with brine in order to lower the freezing point of the catholyte. In known electrolytic pool chlorinators, there is no simple way to add either acid or a brine solution to the cathode chamber for the purposes described above.
Accordingly, it another object of the present invention to provide an electrolytic pool chlorinator including a cathode chamber formed adjacent the lowermost region of the chlorinator housing to maximize the space available to store salt for forming brine, while simultaneously providing easy access to the interior of the cathode chamber for periodic removal of hardness deposits therein and for adding brine to winterize the unit.
Applicant's prior U.S. Pat. No. 4,599,159 discloses a safety feature for switching off the electrical power supply of the electrolytic pool chlorinator upon detecting a stoppage in the flow of pool water that is normally fed to the chlorinator for intermixing with the chlorine gas produced thereby. Upon detecting a stoppage in the flow of pool water, the electrical power supply of the chlorinator is switched off to prevent any further generation of chlorine gas until pool water is again supplied to the chlorinator. However, the thermostatic switch disclosed in applicant's prior U.S. Pat. No. 4,599,159 serves only to switch off the supply of electrical power to the chlorinator; the supply of electrical power provided to the pool pump motor is totally independent from such thermostatic switch, and accordingly, the pool pump motor continues to be supplied with electrical power even though the chlorinator has been turned off by the thermostatic switch, and even though the pool pump has stopped circulating pool water. However, continued application of electrical power to the pool pump motor for an extended time after the pump has either failed or lost its prime can result in damage to the pump.
Accordingly, it is a further object of the present invention to provide an electrolytic pool chlorinator adapted to help prevent damage to the pool pump upon detecting a stoppage in the flow of pool water ordinarily supplied to the chlorinator.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.